Nonreciprocal attenuator



Feb. 9, 1960 s. E. MILLER NoNREcIPRocAL ATTENUATOR Original Filed June 17, 1953 F/G. Z

Feb. 9, -1960 s. E. MILLER NoNREcIPRocAL. ATTENUATOR Orfgi'nal Filed June 17, 1953 4 Sheets-Sheet 2 LOCA TlON OF F IG. /0

/Nl/ENTOR By 5. E. MILLER @n @sa \REs/sT/VE SHEET FIG.v

ATTORNEY Feb-9, 1960 s. E. MILLER NONRECIPROCAL ATTENUATOR Original Filed June 17, 1953 4 Sheets-Sheet 4 055V MA TER/AL /NI/ENTOR S. E. M/LLER @Pff @da A T TORNE Y N ONRECIPROCAL ATTENUATOR Stewart E. Miller, Middletown, NJ., assignor to Bell Telephone Laboratories, Incorporated, New York, N.Y., a corporation of New York Application December 17, 1956, Serial No. 628,906, which is a division of application Serial No. 362,193, June 17, 1953. Divided and this application December 19, 1957, Serial No. 703,937

Claims. (Cl. '333-81) This invention relates to nonreciprocal devices suitable for high frequency or microwave electrical systems and more particularly to nonreciprocal attenuators and/or isolators. This application is a division of my copending application Serial No. 628,906, tiled December 17, 1956, which in turn is a division of my copending application Serial No. 362,193, led June 17, 1953.

An isolator is dened as a device which may be employed to isolate an electromagnetic device from other portions of an electromagnetic wave system, in the sense that waves may be freely transmitted in the direction from the device through the isolator to the system, designated the forward direction, but waves originating outside of the device and traveling in the opposite direction, designated the reverse direction, are attenuated by the isolator to the extent required to prevent deleterious reaction of the system upon the device to be isolated.

Inv a copending application of W. H. Hewitt, Serial No. 362,191, filed June 17, 1953, it has been shown that polarized elements of ferrite and other suitable gyromagnetic materials produce nonreciprocal effects when located asymmetrically with respect to the wave guide structure. Related subject-matter appears in an article by N. G. Sakiotis and H. N. Chait entitled Ferrites at Microwaves which appeared atpages 87 through 93 of the January, 1953, Proceedings of the Institute of Radio Engineers. The nonreciprocal attenuators proposed in the above-noted prior art, are isolators which require relatively strong magnetic fields to operate at the ferromagnetic resonance point for the gyromagnetic material involved. This has required unduly large magnets to supply the biasing field and resulted in unnecessarily bulky and expensive apparatus.

Therefore, it is an object of the present invention to provide an improved nonreciprocal attenuator requiring a much weaker magnetic biasing eld than has heretofore been necessary for directionally selective attenuation components using gyromagnetic elements.

lt has been found that nonreciprocal attenuation may be developed when utilizing gyromagnetic material Without exciting the material to gyromagnetic resonance. Specifically it has been ascertained that a wave guide, either rectangular or round, to which has been coupled a properly polarized gyromagnetic element, will exhibit a permeability greater than one, in that portion of the guide containing the element, to wave energy transmitted therethrough in one direction, while exhibiting a permeability less than one to wave energy propagating therethroughy in the opposite direction. As a consequence the phase velocity of the propagating waves is different for opposite directions of propagation through the guide. By introducing resistive material in the wave guide in the portion of the guide containing the gyromagnetic element, the wave propagating in the direction corresponding to the greater phase velocity experiences greater attenuation since the resistive material having a fixed physical extent constitutes a longer electrical path for the United States Patent ICC wave of greater phase velocity than for the oppositely propagating wave of smaller phase velocity.

In one embodiment in accordance with the invention, the resistive material is dispersed through a dielectric binder substantially filling that portion of the guide containing the gyromagnetic element; in another embodiment the interior walls of the wave guide are coated with resistive material in that portion. In either arrangement the nonreciprocity of the attenuation is enhanced and the reverse to forward loss ratio is increased by utilizing an operating frequency close to the cut-oif frequency of the wave guide.

In the embodiments to be described hereinafter 'in con nection with the drawings these various aspects of the invention are applied to rectangular and circular hollowconductive wave guides, and also to all-dielectric wave guides.

Other objects and certain features and advantages of the invention will become apparent during the course of the following detailed description of the specic illustrative embodiments of the invention shown in the accompanying drawings. v

In the drawings:

Fig. 1 illustrates the magnetic eld configuration for the circular electric TED, mode in a circular Wave guide;

Fig. 2 is a schematic diagram of the magnetic loops in a rectangular wave guide;

Fig. 3 is an idealized plot of the real and imaginary parts of the permeability in a polarized medium of gyromagnetic material;

Fig. 4 shows an arrangement in which a polarized element of ferrite and a resistive sheet are employed to pro,- vide a nonreciprocal microwave attenuator;

Fig. 5 is a plot employed to explain the operation of the device of Fig. 4;

Fig. 6 depicts an arrangement similar to that of Fig. 4 in which a second ferrite element is added to enhance the nonreciprocal effect;

Fig. 7 discloses a wave guide isolator in which two gyromagnetic elements respectively polarized in opposite senses and two resistive vanes are employed;

Fig. 8 shows an embodiment wherein a resistive vane is sandwiched between two elements of ferrite;

Fig. 9 illustrates a eld displacement-resistance isolator in which a dielectric element has been added;

Figs. 10 through 14 illustrate the nonreciprocal attenuation eifect employing ferrite and resistive material as applied to dielectric wave guiding structures;

Fig. l5 represents the cross section of a wave guide having a polarized ferrite element to produce nonreciprocal phase velocity, and wave guide walls which are lossy;

Fig. 16 is a cross sectional view of a wave guide having an asymmetrically positioned ferrite element to produce nonreciprocal phase velocity, and lossy dielectric material filling the balance of the Wave guide;

Figs. 17 through 2l illustrate the use of circularly magnetized paramagnetic elements and resistive vanes in circular waveguides for various of the common modes; and

Fig. 22 is a cross sectional view of an isolator embodying the effects of both field displacement and phase velocity differential.

Referring more particularly to the drawings, Fig. l shows by way of example and for purpose of illustration representative loops of the high frequency magnetic field of the circular electric TEM mode in a circular Wave guide 10 at a particular instant. In this ligure, the arrows 12 through 15 indicate the direction of propagation` of power through thev wave guide and the arrows on the individual closed magnetic loops indicate thepolarity at any particular point in the guide at a given instant. On this basis, it may be noted that the magnetic eld intensity vector at the fixed point 16 in the wave guide 10 will rotate clockwise as the wave propagates through the guide from left to right as indicated by the arrows 12 through 15 of Fig. 1. However, for propagation through the Wave guide in the opposite direction, the circularly polarized components as seen from point 16 will rotate counterclockwise.

In Fig. 2 the pattern of the high frequency magnetic eld of the TElo mode at a ygiven instant in a rectangular wave guide 21 is shown. As the electromagnetic wave propagates from left to right through the guide, it may be observed that the direction of the magnetic intensity vector seen at the xed point 22 in the wave guide will rotate in a counterclockwise direction while that observed at point 23 will rotate clock-wise.

Figs. l and 2 thus demonstrate the presence of nega* tively and positively circularly polarized magnetic components in both rectangular and circular wave guides. The plots of Fig. 3 illustrate the difference in permeability for such positive and negative circularly polarized high frequency magnetic components in a polarized medium of paramagnetic material. These plots are for radio frequency waves in which the magnetic intensity is at right angles to the steady biasing magnetic field and may be derived from a mathematical analysis of D. Polder which appeared in volume 40, pages 99 through 115 of the January 1949 Philosophic Magazine. In this plot of Fig. 3, the real portions of the permeability are shown by the solid lines 31(-|-) and 31( and the imaginary portions are shown by the dotted lines 32(I-) and 32(-). Concerning the real portions, the negative (one which rotates counterclockwise when looking along a north-to-south pole biasing magnetic vector) circularly polarized component 3\1() has an increasing permeability as the biasing magnetic intensity is increased, and the positive circularly polarized component 31(|) experiences al reduction in permeability for a similar increase in biasing magnetic intensity, at magnetic ields below ferromagnetic resonance, indicated at Hr on Fig. 3. More specifically, the negative component has a permeability greater than one while the positive component has a permeability less than one.

One physical explanation which has been advanced to explain this phenomenon involves the assumption that the ferromagnetic material contains unpaired electron spins which tend to line up with the applied magnetic eld. These spins and their associated moments can be made to precess about the line of the magnetic eld, keeping an essentially constant component of magnetic moment in tihe applied ield direct-current direction but providing a magnetic moment which may rotate in a plane normal to the steady magnetic field direction. These magnetic moments have a tendency to precess in one angular sense, but strongly resist rotation in the opposite sense. This tendency of a spinning element to consistently precess in one angular sense is familiar to anyone who has watched a top wobble before stopping. Considering the interaction bet-Ween the oppositely polarized components of high frequency magnetic intensity and the magnetic moments, it is clear that one of the circularly polarized components will be rotating in the easy angular sense of precession of the magnetic moments and the other component Iwill be rotating in the opposite sense. When the high frequency magnetic intensity is rotating in the same sense as the preferred sense for precession of the magnetic moment, it will couple strongly -with the magnetic moment and drive it into precession. When the high frequency magnetic intensity is rotating in the opposite angular sense, however, very little coupling or interaction between the higfh frequency magnetic intensity and the magnetic moments takes place.

While this diiference in coupling and consequent df-v y of the permeability for the positive circularly polarized component has a sharp maximum. Although attenuation varies with the imaginary portion of the permeability, phase velocity and electromagnetic eld displacement vary with the real portion of the permeability. My copending parent application, mentioned above, deals primarily with embodiments which function with respect to the imaginary portion of the permeability. The embodiments to be disclosed hereinafter, however, operate responsively to the real portion of the permeability. Accordingly these embodiments are nonreciprocal because the real permeabilities experienced by positive and negative magnetic wave components are respectively dilferent.

The device of Fig. 4 is a nonreciprocal attenuator or isolator utilizing the field displacement eifect. Considering the device of Fig. 4, the hollow rectangular conducting section of wave guide 41 has an elongated element of paramagnetic material 42 against one of the narrower side walls. In addition a resistive strip 43 is mounted on the inner side of the paramagnetic element 42 within the wave guide 41. An electromagnet 44 magnetizes the element 42 transversely, as shown. As is illustrated in Fig. 5, the electric eld distribution `521 of the electro magnetic wave which is propagated in one direction through the wave guide (shown in dashed line) is asym metrically distorted so that it hulges toward the paramagnetic element to a substantial degree, while the iield distribution 52 of the oppositely propagated electromagnetic wave, also asymmetrically distorted, is bulged away from the ferrite element to a lesser degree. The reason for this is that the transversely magnetized element of ferrite presents a permeability greater than one for wave propagation into the plane of the paper (whereby the concentration of the held distribution in the ferrite is increased) and less than one for a wave traveling out of the plane of the paper (whereby its eld distribution concentration is decreased in the ferrite). At the position of the resistance sheet a larger eld will be present for wave propagation into the plane of the paper (dotted curve of Fig. 5) than will Vbe present for the wave propagating out of the plane of the paper (solid curve of Fig. 5). Thus the loss will be much lower for the wave propagating out of the plane of the paper than for the wave propagating into the plane of the paper.

The element 42 of the device of Fig. 4 is made from a paramagnetic material which has low conductivity. The conductivity ranges should be moderately low in order to prevent undue distortion of the electromagnetic iield, and the samples shouldk preferably have a resistance greater ohm-centimeters, although operable devices could be made with resistivities as low as l0 ohm-centimeters. Any of a number of ferromagnetic materials which eachcomprise an iron oxide in combination with one or more bivalent metals, such as nickel, magnesium, zinc, manganese or other similar material have proved to be satisfactory. These materials combine with the iron oxide in a spinel structure and are known as ferromagnetic spinels or as polycrystalline ferrites. In accordance with the usual practice, these materials are first powdered and then molded with a small percentage of plastic material such as Teon or polystyrene. As a specific example, the element 42 may be of nickel-zinc ferrite of the approximate chemical formula prepared as noted above. In addition, commercially available samples of ferrite, and finely powdered conducting ferromagnetic dus't in aninsulating binder may be employed. By way of inclusion but not of limitation, the phrase paramagnetic material having low conductivity is to? be construed as applying to the foregoing types of material. In addition, as employed inthe present application and claims, the term gyromagnetic medium is intended to apply to all materials having magnetic properties of the type disclosed in the above-mentioned article by Polder, and discussed above in conjunction with Fig. 3.

In the cross sectional view of Fig. 6 the coordinates employed in Fig. 5 are indicated, and an arrangement employing two similarly biased elements 61 and 62 of ferrite at opposite sides of the rectangular conducting wave guide 63 is set forth. In addition, a resistive vane 64 is again mounted on the inner side of one of the ferrite elements 62. With the ferrite elements located on opposite sides of the wave guide but magnetically biased in the same sense, one ferrite element exhibits a permeability greater than one for waves in one direction of propagation and the other ferrite exhibits a permeability greater than one but for waves propagating in the opposite direction. In this instance, therefore, one ferrite element distorts the field pattern for one direction of propagation in one lateral direction and the other ele- Iment tends to distort the oppositely propagating wave in the opposite lateral direction. This increases the asymmetry of the field distributions and thus enhances the difference in field strengths at the resistive vane 64 for the two directions of propagation and consequently emphasizes the nonreciprocal attenuation effect.

Where a symmetrical ferrite structure isl used, as in Fig. 46, the resistive material should be placed in only one of the two ferrite strips, or if it is placed in both strips the sense of the biasing magnetic field on one `of the strips should be reversed. Accordingly Fig. 7 illustrates this latter arrangement. Specifically the isolator of Fig. 7 includes the Wave guide 71, the two gyromagnetic elements 72 and 73 which are polarized in opposite senses, respectively, and also includes the resistive strips or coatings 74 and 75 mounted, respectively, on `the gyromagnetic elements 72 and 73. The physical reason underlying the latter arrangement is that the field distribution for one direction of propagation will tend to be squared up and thus have substantial components near the side walls of the guide where they will be attenuated by the resistive material, while the field distribution for the opposite direction of propagation will be concentrated toward the open central portion of the guide. This may be understood by considering that with the gyromagnetic elements biased in opposite senses each of them will exhibit a permeability greater than one for the same direction of wave propagation, while each of them will exhibit a permeability less than one for waves propogating in the opposite direction. Therefore, despite the fact that both field distributions will be symmetrical across the wave guide, the field distribution of waves for one direction-of propagation will be distorted differently from that for the opposite direction.

Figs. 8 and 9 are cross sectional views of arrangements representing slight Variations of the general type of arrangement illustrated by the structures of Figs. 4 and 6. In Fig. 8 the resistive vane 81 'is sandwiched between two thin ferrite elements 82 and 83 and the three elements are all placed at one side of the rectangular wave guide 84 to provide a nonreciprocal attenuator.

In Fig. 9 as in Fig. 4 the paramagnetic element 91 has a resistive vane 92 mounted thereon and the two elements are located at one side of a conductive wave guide 93 with a polarizing magnetic field applied to the paramagnetic element. In Fig. 9, however, a block of dielectric material 94 is provided at the opposite side of wave guide 93 to equalize some of the dielectric effect of the ferrite, to enhance the nonreciprocal loss effect.

Figs. l0 through 13, inclusive, illustrate the application of the foregoing principles of field displacement isolation to dielectric wave guides of the type disclosed in A. G. Fox application, Serial No. 274,313, led March 1, 1952, 110W Patent 2,794,959, granted Iune 4, 1957.

In Fig. l0, the dielectric guideis made up of the elongated dielectric element 101, the ferrite strip 102 and the tapered resistive vane 103 which all have the same functions as the comparable elements of Fig. 4. In the dielectric guide structures, however, because much of the electromagnetic wave energy is propagated in a field which is external to the guide, it is convenient to have the resistive vane 103 mounted on the outer surface of the paramagnetic strip 102.

Fig. 11 is a cross section taken along lines 11--11 of Fig. 10 and constitutes another view of the three com-a ponent elements.

Fig. 12 is a cross sectional view of the dielectric guide equivalent of the conducting wave guide arrangement of Fig. 6. In Fig. 12, the waves are guided by the dielectric element 121 and the two matching ferrite elements 122 and 123 which are on either side of it. These ferrite strips also shift the electromagnetic field distribution in much the same manner as set forth in Fig. 5, and the resistive vane 124 attenuates waves propagating in one direction to a greater extent than the oppositely propagated waves.

Fig. 13 is a cross sectional view of the dielectric guide equivalent of the conducting wave guide arrangement of Fig. 7. In Fig. 13, the waves are guided by the dielectric element 131 and the oppositely magnetically biased ferrite elements 132 and 133 which are on either side of it. These ferrite strips also symmetrically shift the electromagnetic field distribution in much the same manner as set forth with respect to Fig. 7, and the resistive vanes 134 and 135 mounted respectively on ferrite elements 132 and 133 attenuate waves propagating in onedirection to a greater extent than the oppositely propagated waves.

In the cross sectional view of Fig. 14, the dielectric .material between the two ferrite elements of Fig. 12 has been dispensed with and the isolator structure comprises a simple transversely magnetized rectangular strip of ferrite 141 which guides the waves and also shifts the field patterns in the requisite manner. A resistive vane 142 is mounted on one of the narrow outer sides of the ferrite strip 141.

The resistive vanes have been shown in the preceding arrangements illustrated by Figs. 4 through 14, inclusive,

as mounted on the ferrite strips. This is merely for con` venience and the resistive elements may be placed at other points in the structure. The important matter is to have the resistive vanes located at the point or points where there is greater difference between the squares of the electric fields for the two directions of propagation. Instead of separate resistive vanes, the resistive material may be mixed with the composite ferrite and insulating material in any of the devices of Figs. 4 through 13, inclusive.

Because of the difference in phase velocities for the tWo directions of propagation for many of the wave guide structures disclosed in the present application, other types of isolators such as are illustrated in the cross sectional views of Figs. 15 and 16 can be constructed. Specifically, in the vicinity of cut-off, a difference between metallic Wall losses for the two directions of transmission will exist due to the fact that the Wave propagating in one direction will be closer to cut-off than the other.

In Fig. 15, rectangular wave guiding structure 151 is provided with the usual asymmetrically located, transversely magnetized element of ferrite material 152, and is also provided with an internal layer 153 of relatively high resistivity, such as a painted layer of aquadag, which has a thickness approximating the skin depth. When a section of the wave guiding structure such as is shown in Fig. l5 several wavelengths long is coupled to a micro- Wave source having a frequency slightly above the cut off frequency of the Wave guide structure, the attenuationthrough the unit will be much greater for one direction of transmission than for the other. In Fig. 16 the lossy dielectric material 161 in combination With the wave guide 7 152 and polarized `ferrite elementy l163 serve to yield the same elect as the device of Fig. 15 when a similar length is operated in the same manner as set forth above. The dielectric material may be made up of dielectric material such as polystyrene having finely divided particles of carbon dispersed throughout its volume.

Figs. 17 through `20, inclusive, illustrate, in cross sectional views, resistance sheet field-displacement type isolators for circular wave guides, which operate on much the same principles discussed above in connection with the rectangular wave guide structures illustrated in Figs. 4 through 7, inclusive. The similarity becomes apparent on considering Figs. 1 and 2 in their relation to Fig. 3.

The` structure of Fig. 17 is designed to be used with the TEM mode in the circular Wave guide 171. Within this wave guide, the ferrite liner element 172 shifts or displaces the electric eld configuration toward the resistive sheet 173 for a first direction of propagation and away from the resistive sheet for the opposite direction of propagation, so that the resistive vane 173 attenuates the wave propagating in the first direction to a substantially greater extent than the oppositely propagated waves. The circumferential field in the ferrite liner 172 of Fig. 17 may be obtained by the permanent magnetization of the core, by a coil threaded through the liner or by any other suitable method. As may be observed by correlating Figs. l and 17, the circularly polarized components of the high frequency magnetic field lie in radial planes which are perpendicular to the circumferential biasing magnetic field in the cylindrical ferrite liner 172. Considering electromagnetic waves of the TEM mode, propagating in opposite directions through the wave guide 171, it is clear that the circularly polarized components of the radio frequency magnetic intensity for the opposite directions of propagation will have opposite senses of rotation with respect to the steady magnetic field and thus that the permeabilities experienced by the oppositely directed Waves will differ as indicated by the plots of Fig. y3. As a consequence the above-mentioned shifts or dis placements in electric field configurations result.

In the device of Fig. 18, the ferrite liner 172 and the resistive sheet 173 within the circular wave guide 171 are assisted in the field displacement action by the central hollow coaxial ferrite element 181 which is magnetized in the same angular sense as the outer ferrite core 172 by passing direct current through a centrally located conductor 182. This central ferrite element 181 acts in much the same manner as the second ferrite element in Fig. 6 to displace the field intensity toward the resistive sheet for a first direction of propagation While displacing the field intensity for the other direction of propagation away from the resistive sheet, thus cooperating with the outer ferrite element 172 to create a greater differential loss at the resistive sheet 173.

Figs'. 19 and 20 illustrate resistance sheet field-displacement isolators for the TEU mode.

In Fig. 19, a semicylindrical liner element '191 of ferrite overlies a portion of the inner surface of the circular wave guide 192. The electromagnet 193 provides the magnetic field for biasing the element 191 of ferrite. Electromagnet 1'93 is shown energized by a steady biasing current from direct-current source 194. As a consequence of resistive sheet 195 mounted on ferrite element 191, the unit provides nonreciprocal attenuation for vertically polarized electromagnetic Waves 196 due to the field displacement eifect, and will exhibit nonreciprocal phase displacement properties for horizontally polarized waves 197.

In the isolator of Fig. 20, a resistive sheet 2111 is mountedon one internal surface of the cylindrical ferrite liner 202, which in turn is supported bythe inner surface of the circular conducting wave guide 2&13. The biasing' magnetic lield for the core 202 is applied to the top andvbottorn of the cylindrical core 20'2 as illustrated by the branching arrows. When the TEM mode is vertically polarized s indicated by the s'olid arrow 196 at the center of the wave guiding passageway, the 4structure'of Fig. y2() bears much the same relationship to that of Fig. 1 9 as' the structure ofl Fig. 6 does to ythat of Fig. 4, and the field-displacement is enhanced. The structure of Fig. 20 does not yield a nonreciprocal phase shifting effect with any polarization of the TEU mode, and even has reciprocal loss characteristics' when the TEM mode is horizontally polarized as indicated by the dashed arrow 197 of Fig. 2G.

Fig. 21 illustrates a resistance sheet field-displacement isolator for the TE21 mode having a eld orientation as illustrated by arrows 211. This device, for the TE21 mode is analogous to the structure of Fig. 20 Ifor the TEU mode, and thus has the single resistive vane 212 mounted on the hollow ferrite cylindrical liner 213 within the conducting guide 21'4. The magnetic field is applied to the core at 90- degree intervals about the circumference of the liner, as shown, with the two north poles opposing one another and the two south poles also in opposition. With the foregoing geometry, the` field distribution for one direction of propagation will be displaced toward the resistive element 212 and the field distribution for the opposite direction of transmission willbe shifted away from it, so that the result will be the nonreciprocal attenuation feature characteristic of all of these field-displacement isolators. With the foregoing examples as a guide, other resistance sheet field-displacement isolators can readily be constructed for other modes.

ln Fig. 22 va nonreciprocal attenuating device is disclosed in which both the lfield-displacement and phase velocity ldifferential effects discussed above are utilized cumulatively to produce desired nonreciprocal attenuation effects.v

In Fig. 22 the outer circular conducting wave lguide' 221 eri-closes a number of concentric cylinders of various materials. Specically, proceeding inwardly there is a thin layer of high resistance material 222, a ferrite cylinder `223 of substantial thickness, a resistance sheet 224, a very thick cylinder '225 of dielectric material containing a slight amount of lossy material distributed therethrough, a ho1- low cylinder of permanently magnetized ferrite 226 and a central cylinder of dielectric material 227 similar in composition to cylinder 225. A circumferential magnetic eid is applied to the outer ferrite cylinder 223 by means of a coil 22S in the manner taught in my above-mentioned parent application. The magnetization in this outer cylin der 223 may be from a suitable source of direct current 23?. The double pole double throw switch 229 facilitates reversing the polarity of the magnetization in the outer ferrite cylinder 223. y

Considering the possible modes of operation of the structure of Fig. 22 when energized in the TEM mode, it may be noted that with the sense of peripheral magnetization in the outer cylinder 223 the same'as that of the permanently magnetized inner cylinder 226, these elements together with the lossy material 223 and the resistive sheet 224 will constitute a field-displacement isolator. With senses of the fields being the same, however, the inner cylinder will have 'increased permeability for one direction of propagation and the outer cylinder will have increased permeability for oppositely propagated waves, and the net nonreciprocal phase shift will not be unduly great. v

When the magnetic eld is reversed and the microwave energy is at a frequency just above cutoff, the nonreciprocal attenuation factors due yto iield-displace ment and phase velocity difference are Combined. Initially,` it may be noted that with the inner and outer ferrite cylinders magnetized in opposite circumferential senses, they will both exhibit increased permeability for the same direction of propagation of waves of the TEM mode. In the direction of increased permeability the wave guide is operating closer to cut-off and the losses d-ue to the lossy dielectric '225,v 227 and the lossy inner coating 222 of the guide 221 are increased. Simultaneously, field-displace ment occurs bringing resistance sheet 224 into elect for nonreciprocal attenuation.

Although many of the devices have been disclosed specifically, as for example by stating that the paramagnetic element is of ferrite or that the applied biasing magnetic `field is steady, these specific disclosures are merely exemplary and are not to be considered limiting. Speciiically, other types of paramagnetic material having low conductivity such as were discussed hereinabove may be used in any of the disclosed devices. In addition it might be noted that the present isolators may involve the use of tapered transitions at the point where the nonreciprocal element is coupled to standard sections of wave guide.

It is to be understood that the above-described arrangements are illustrative of the application of the principles of the invention and no attempt has been made to exhaustively illustrate all possible embodiments thereof. Numerous other arrangements, obviously, may readily be devised by those skilled in the art without departing from the spirit and scope of the invention.

What is claimed is:

l. In an electromagnetic wave transmission structure, a first means for producing a phase velocity dilerential in a portion of said structure for opposite directions of propagation of electromagnetic wave energy therethrough, and a second means comprising a high loss producing resistive material dissipative of energy in the form of conduction currents disposed at least at a region within said portion wherein the electric eld components of said electromagnetic wave energy are of the same intensity for both said opposite directions of propagation.

2. In combination, a wave guide, a rst means for producing a phase velocity dilerential in a portion of said wave guide for opposite directions of propagation of electromagnetic wave energy therethrough, said lrst means comprising a low loss element of magnetically polarized material exhibiting the gyromagnetic effect at the frequency of said wave energy and a second means comprising a high loss element of resistive material coupled to said wave guide and disposed at a region within said por tion wherein the electric eld components of said wave energy are of equal amplitude for both said opposite directions of propagation.

3. A combination as recited in claim 2 wherein said element of said second means comprises a thin hollow liner overlaying the inside surface of said Wave guide in said portion.

4. A combination as recited in claim 2 wherein said second means comprises resistive material dispersed throughout a dielectric binder substantially filling said portion of said wave guide.

5. A combination as recited in claim 2 wherein said wave guide has a round transverse cross section, said first means comprises a hollow gyromagnetic cylinder coaxially disposed within said round wave guide, said gyromagnetic cylinder being circumferentially magnetically polarized.

6. A combination as recited in claim 5 including a second cylinder of gyromagnetic material coaxially disposed within said round guide, said second cylinder being circumferentially magnetically polarized, the sense of the magnetic polarity of said second cylinder being opposite to that of said iirst cylinder.

7. A combination as recited in claim 2 including means for exciting said wave guide with electromagnetic waves at a frequency near the cut-oil frequency of said wave guide.

8. ln combination, a wave guiding structure having a substantially quadrangular transverse cross section for guiding radio-frequency wave energy, a low loss vane of magnetically polarizable material exhibiting the gyromagnetic effect at said radio frequency disposed asymmetrically within said transverse cross section and magnetically biased in a direction parallel to the narrow walls of said wave guide to produce a phase velocity differential within a portion of said wave guide for opposite directions of propagation of wave energy therethrough, and high loss resistive material in a form having a transverse extent measured in the direction parallel to the wide walls of said guide at least as great as the transverse extent of said gyromagnetic element measured in Said same direction, said resistive material being located within said portion of said guide.

9. A combination as recited in claim 8 including means for exciting said wave guide with electromagnetic waves at a frequency near the cut-off frequency of said wave guide.

l0. A combination as recited in claim 8 wherein a1: least a portion of said resistive material conforms to a thin planar region parallel to said wide walls.

References Cited in the tile of this patent UNITED STATES PATENTS 2,743,322 Pierce et al. Apr. 24, 1956 2,748,353 Hogan May 29, 1956 2,764,743 Robertson Sept. 25, 1956 2,784,378 Yager Mar. 5, 1957 2,787,765 FOX API'. 2, 1957 2,834,947 Weisbaum May 13, 1958 FOREIGN PATENTS 674,874 Great Britain July 2, 1952 

